This invention relates to analog-to-digital converters, and more particularly, to an improved dual slope analog-to-digital converter.
Dual slope analog-to-digital converters divide the stages within a conversion sequence into three equal time periods of magnitude generally equal to the time required to count through all the states of a digital counter. The first time period is devoted to zeroing the system; the second time period is devoted to integration with the analog voltage, representing the measured parameter, switched into the circuit; and, the third time period devoted to integration with the analog reference voltage, representing full scale of the measured parameter, switched into the circuit. Conventionally, during the first time period, the storage element; i.e., a capacitor, is discharged to 0 volts; during the second and third time periods, the measured parameter voltage is compared to the full scale reference voltage and the results (represented by the counter value at a particular instant) latched in digital form which may be stored, displayed and/or utilized for some other desired purpose.
For most applications, however, complex decoding of the count value is required before the value can be utilized or displayed. Furthermore, where multiple scales (i.e., metric, English, etc.) are utilized, such complex decoding is required for each scale.
A further object of the invention is to provide an analog-to-digital converter which generates easily-decodeable results for use and/or display on multiple scales (i.e., metric, English, etc.).
It is another object of the invention to provide an analog-to-digital converter which is capable of being integrated as a semiconductor circuit utilizing I.sup.2 L techniques.
Still another object of the invention is to provide an analog-to-digital converter which is integratable on a single substrate with digital circuitry to provide a complete analog-to-digital system on a single semiconductor chip.
Yet another object of the invention is to provide an analog input stage for a portable, battery-operable digital thermometer.